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INTRODUCTION

An ectopic or extrauterine pregnancy is one in which the blastocyst implants anywhere other than the endometrial lining of the uterine cavity. As such, they account for 1 to 2 percent of reported pregnancies in the United States (Zane, 2002). With the advent of a sensitive and specific radioimmunoassay for the β-subunit of human chorionic gonadotropin (β-hCG), combined with high-resolution transvaginal sonography (TVS), the initial presentation of a woman with an ectopic pregnancy is seldom as life threatening as in the past. Nevertheless, ectopic pregnancies remain an important cause of morbidity and mortality in the first trimester of pregnancy in the United States.

EPIDEMIOLOGY AND INCIDENCE

Reported ectopic pregnancy incidence rates are not as reliable as in the past. The dramatic improvements in diagnosis and outpatient treatment protocols render national hospital discharge statistics invalid. That said, one evaluation within the Kaiser Permanente system from 1997 to 2000 estimated a rate of 20.7 per 1000 pregnancies (Van Den Eeden, 2005). More recently, Hoover and colleagues (2010) queried a large claims database for women aged 15 to 44 years who were privately insured in the United States between 2002 and 2007 and calculated a rate of 6.4 per 1000 pregnancies. However, this reduction in ectopic pregnancy rate might not accurately reflect cases occurring in higher-risk, lower-socioeconomic, uninsured populations. Namely, Stulberg and associates (2014) reviewed 2004 to 2008 Medicaid claims data and confirmed that black women were 46 percent more likely to experience an ectopic pregnancy compared with white women. They reported a rate of 14.0 per 1000 pregnancies in the 14 states evaluated.

ETIOLOGY AND RISK

An appreciation of risk factors for ectopic pregnancy may lead to a more timely diagnosis. As summarized in Table 8-1, documented tubal pathology, surgery to restore tubal patency, and tubal sterilization carry the highest risks for fallopian tube obstruction and subsequent ectopic pregnancy. A woman with two prior ectopic pregnancies has a 10- to 16-fold increased chance for another (Barnhart, 2006; Skjeldestad, 1998).